#include <stdio.h>

/* 全局变量声明 */
int a = 20;

int main() {
    /* 在主函数中的局部变量声明 */
    int a = 10;
    int b = 20;
    int c = 0;
    int sum(int, int);

    printf("value of a in main() = %d\n", a);
    c = sum(a, b);
    printf("value of c in main() = %d\n", c);

    return 0;
}

/* 添加两个整数的函数 */
int sum(int a, int b) {
    printf("value of a in sum() = %d\n", a);
    printf("value of b in sum() = %d\n", b);

    return a + b;
}